I have been taking get ssri for 3years so what will its long usage side effects?

Should be safe.: The SSRIs are considered safe to take in the long term, certainly safer than other medications which can be quite habit-forming and addictive. But, it is known that within 6 months to 2 years generally, they can stop working, so if you feel it's not working anymore then there's no sense in taking this particular SSRI anymore - seek an alternative if this is the case.